The present invention relates to a switch chamber for a vacuum switch including a housing having at least one insulating tube, and in which a stationary contact pin supports the switch chamber and mounts a stationary contact, and a terminating cover connects the insulating tube with the contact pin in a vacuum-tight manner. In this type of switch chamber a movable contact has a frontal face positioned adjacent the stationary contact and is movable approximately in the axial direction of the insulating tube. A bellows forms a vacuum-tight connection between the movable contact and the housing. In the switched-on position of the vacuum switch the frontal face of the movable contact contacts the stationary contact under action of a contact spring force and the shock stresses generated when the vacuum switch is turned on are transferred to the housing by the terminating cover.
Such a switch chamber is disclosed in U.S. Pat. No. 3,082,307 which shows, with reference to FIG. 6 therein, a chamber having a stationary switch contact which is fastened to a tubular contact pin which, in turn, has a vacuum-tight connection with a tubular isolator by way of an intermediate member or terminating cover that is curved at its outer and inner ends. According to the drawing of the cited patent the isolator is made of glass into which the outer end of the intermediate member is melted while the inner end is connected with the exterior of the contact pin in the manner of a collar, presumably by soldering. The cited reference does not disclose anything about the mechanical characteristics of the intermediate member or about problems arising in connection with this component.
The above described prior art switch chamber is obviously intended for a relatively low operating and test voltage. The tubular isolator is actually two isolator parts having small dimensions with a metal housing disposed between them. The housing and intermediate members terminating the isolators have relatively large dimensions. There is a small annular gap between the contact pin and the isolator which results in the elastic intermediate member, in spite of its curvature, reacting to mechanical deformations with a high spring constant. The shocks transferred from the stationary contact to the housing during switching-on generate axially directed mechanical vibrations in the housing which may result in great stresses on the isolator, primarily in the melted connection zone of the intermediate member.
Due to advance ignition in thee-phase high voltage switching equipment, currents occur before there is any galvanic contact between the switch contacts. In the case of a short-circuit, these currents generate great, laterally acting forces. If the short-circuit currents are high, these forces may lead to lateral displacement of the contact pin and to eccentric connection between the contacts themselves, which may also result in twisting forces relative to the axial axis of the switch chamber.
The prior art switch chamber is not designed for such stresses since the curved intermediate member acts as a clamped-in carrier at both its inner and outer ends, i.e. transfers a clamping moment to the isolator. However, for the isolator, this type of stress constitutes a particular danger since dynamic operating stresses are added to the shrinkage stresses caused by manufacturing processes.